This Direct Phase II SBIR Grant application seeks support to continue the preclinical development of a paradigm-changing therapeutic for rheumatoid arthritis (RA). RA is a chronic, debilitating systemic disease that affects 0.5 to 1% of the population worldwide. Despite the advent of biologic therapies, it is broadly recognized that there remains a significant unmet need for more effective and safer RA treatments since approximately 1/3 of RA patients are refractory to all existing therapies and current drugs are limited by severe adverse side effects. Oryn Therapeutics, LLC (the company) will conduct IND-enabling studies that exploit the discovery of a new class of macrocyclic immunomodulating peptides, termed theta-defensins (?-defensins), expressed in leukocytes of Old World primates. ?-defensin expression ceased before the emergence of humans, gorillas, and chimpanzees. Thus, the company has embarked on the development of a synthetic version of a natural ?-defensin, termed ORTD-1, as a retro-evolutionary biologic pharmaceutical for RA. SBIR Phase I-equivalent studies suggest that ORTD-1 may be utilized for RA treatment in humans without the adverse side effects of currently employed RA drugs. Scalable protocols for ORTD-1 synthesis have been developed, enabling the testing of multi-gram batches of cGMP ORTD-1. With this material we showed that ORTD-1 is highly effective in two animal models of RA, and the cyclic peptide is more effective than methotrexate or etanercept (Enbrel(r)) in arresting and reversing autoimmune arthritis in rats. ORTD-1 is non- toxic, has unexpected pharmacokinetic (PK) properties, and is non-immunogenic. Further, ORTD-1 has shown no evidence of immunocompromising immunosuppression, one of the adverse side effects of current RA biologics. The company proposes focused studies outlined in two Specific Aims to further the development of ORTD-1 through filing of an IND application with the FDA. In Aim 1, we will i) refine a recently developed ORTD-1 ELISA for use in GLP toxicokinetic studies, ii) perform multi-dose ORTD-1 PK studies in rats, iii) conduct PK/pharmacodynamic studies in the rat pristane-induced arthritis model, and iv) determine metabolism and route of elimination of 14C-ORTD-1 administered to rats. In Aim 2, we will conduct IND-enabling GLP toxicity and toxicokinetic studies of injectable ORTD-1 in rats and beagle dogs. The development plan also includes ORTD-1 formulation studies, which are already underway, and genotoxicity studies. The development plan includes preparation of the pre-IND Briefing Document and the pre-IND meeting itself in the 01 year. A key milestone for the proposed studies will be filing of an IND application for ORTD-1 as an RA therapeutic, by the end of this two-year project.